It is well known that limiting the exposure of an oxygen sensitive product to oxygen maintains and enhances the quality and shelf life of the product For instance, by limiting the oxygen exposure of an oxygen sensitive food product in the packaging system, the quality of the food product is maintained by minimizing nutrients loss, slowing enzymatic and lipolytic oxidation, preventing photolytic degradation, and reducing spoilage. In addition, such packaging also keeps the product in inventory longer, thereby reducing restocking costs, and costs incurred from waste.
One means for limiting the exposure of a product to oxygen involves incorporating an oxygen scavenger into the packaging structure itself. This achieves a more uniform scavenging effect throughout the package. This may be especially important where there is restricted air circulation inside the package. In addition, such incorporation can provide a means of intercepting and scavenging oxygen as it passes through the walls of the package (herein referred to as an "active oxygen barrier"), thereby maintaining the lowest possible oxygen level throughout the package.
Oxygen scavengers that can be incorporated into a film structure are disclosed in U.S. Pat. Nos. 5,310,497, 5,350,622 and 5,399,289 (Speer et al.), and a method of initiating oxygen scavenging generally is disclosed in U.S. Pat. No. 5,211,875 (Speer et al.). All of these four patents are incorporated herein by reference in their entirety. According to U.S. Pat. No. 5,350,622, oxygen scavengers are made of an ethylenically unsaturated hydrocarbon and transition metal catalyst. The preferred ethylenically unsaturated hydrocarbon may be either substituted or unsubstituted. The "oxygen scavenger" materials disclosed by Speer et al. are compounds which consume, deplete or reduce the amount of oxygen from a given environment.
Other oxygen scavengers which can be incorporated into a film structure are disclosed in PCT patent publication WO 94/12590 (Commonwealth Scientific and Industrial Research Organisation). These oxygen scavengers include at least one reducible organic compound which is reduced under predetermined conditions, the reduced form of the compound being oxidizable by molecular oxygen, wherein the reduction and/or subsequent oxidation of the organic compound occurs independent of the presence of a transition metal catalyst. The reducible organic compound is preferably a quinone, a photoreducible dye, or a carbonyl compound which has absorbence in the UV spectrum.
Oxygen scavengers are useful in modified atmosphere (MAP) and barrier packaging environments. However, oxygen scavengers often require, or at least benefit from, triggering in order to activate the oxygen scavenging properties.
In U.S. patent application Ser. No. 08/691,829 filed Aug. 2, 1996, now abandoned incorporated by reference herein in its entirety, an apparatus is disclosed which is beneficial in triggering oxygen scavenger films. This apparatus is especially useful when employed in a food processing plant or other facility where the triggering apparatus is located near a packaging machine. Thus disposed, an oxygen scavenger film can be triggered shortly before, and perhaps just a few seconds before, the film is used to package a food or other oxygen sensitive product.
Most packaging areas in food manufacturing facilities, such as meat processing plants, are typically kept at relatively low temperatures, on the order of 40.degree. F. to 50.degree. F.
The inventors have found that at these low temperatures the induction period (the time between exposure of an article to actinic radiation or other triggering mechanism, and the onset of oxygen scavenging by the article) can undesirably lengthen.
Also, at these low temperatures, the rate at which the triggered article will oxidize can be undesirably decreased.
Packaging materials containing an oxidizable organic compound exhibiting lengthy induction times must be held by the processor in inventory for a sufficient period of time before use. Thus, a longer induction time can be costly to the processor by resulting in increased inventory. If the packaging step occurs shortly after exposure to the triggering means, a delayed induction can mean that the oxygen sensitive product is disposed in the package for some time without the benefits of oxygen scavenging. In some cases, foods have a very high affinity to oxygen. This can result in a shortened shelf life for the package and/or reduction in product quality, because oxygen inside the package, or entering the package from the outside environment, can deleteriously affect the quality of the packaged product before the onset of oxygen scavenging. There is thus a competitive relationship for the available oxygen between the food and the packaging material.
Lowered oxygen scavenging rate can also have an adverse effect on product shelf life and/or quality. If the oxygen in the head space of a package is not removed quickly enough, then the detrimental effects of this oxygen on the packaged product (rancidity, spoilage due to growth of microorganisms, color change, etc.) are increased.
One possible solution to these problems is to use more of the oxygen scavenger, or if present more of the photoinitiator and/or catalyst, in the article. However, it has been found that although additional loading of the oxygen scavenging material in the article can increase the scavenging capacity of the article, it does not appreciably increase the rate at which the article scavenges.
A second possible solution is the use of a larger triggering unit of the type generally disclosed herein and in U.S. patent application Ser. No. 08/691,829, now abandoned. However, using additional banks of UV lamps, or otherwise increasing the level of actinic radiation incident on the film, does not necessarily result in an increase in scavenging rate in the triggered article.
Also, making the triggering unit larger is not desirable. On the contrary, it is much more convenient for the processor to use a unit which is small in size, in order to save valuable space in the facility, and in order to more easily physically integrate the triggering unit with an associated packaging machine.
The inventors have discovered that benefits in induction period and scavenging rate can be obtained by raising the temperature of the environment in which the triggering unit is located. One way to take advantage of this discovery would be to increase the overall ambient temperature of the processing/packaging facility in which the triggering and packaging operations occur. However, in the case of food, and especially meat packaging, this is not a feasible alternative because of the need to process and package these products in an overall relatively cool environment.
The inventors have found that benefits can be obtained by providing a means for heating, the means for heating disposed within a triggering chamber. The invention provides an effective method of and apparatus for triggering an article containing an oxidizable organic compound so as to result in a relatively short induction period, and enhanced oxygen scavenging rate, compared with an oxygen scavenging method and apparatus without the benefit of the invention.
Locating the means for heating inside the triggering chamber provides the additional benefit of warming the radiation bulbs to reduce startup time and thereby increase overall production rates.
The method and apparatus preferably allow the article to be triggered immediately prior to use during packaging of an oxygen sensitive product; and preferably provide a compact triggering means.
Preferably, an apparatus is provided which is readily incorporated in-line into existing packaging systems for triggering articles at or immediately prior to packaging.